The present invention relates to a subject illuminating device, and more particularly to a subject or original illuminating device including a linear array of optical fibers having respective ends for emitting illuminating light toward a subject or original, which ends are spaced progressively closer from the center toward the opposite ends of the array for shading correction of image information from the subject.
In printing and platemaking industries, image scanning recording/reproducing systems are widely used for electrically processing image information on subjects or originals to produce film plates with a view to simplifying the operation process and increasing the image quality.
Such an image scanning recording/reproducing system is basically constructed of an image reading device and an image recording device. In the image reading device, image information on a subject which is fed in an auxiliary scanning direction is scanned in a main scanning direction by a photoelectric transducer which converts the image information to an electric signal. Then, the image information which has been photoelectrically converted by the image reading device undergoes various processes such as for gradation correction, profile emphasis, and the like dependent on platemaking conditions in the image recording device. Thereafter, the image information thus processed is converted to a light signal represented by a laser beam, which is applied to an image recording medium made of a photosensitive material such as a photographic film to record the image information thereon. The image recorded on the image recording medium is then developed by an image developing device, and the developed image recording medium is used as a film plate for printing operation or the like.
The image reading device employs a charge-coupled device (hereinafter referred to as a "CCD") composed of a linear array of photoelectric transducers along a main scanning line for scanning the image information on the subject at high speed. The subject or original is illuminated along the main scanning line by illuminating light, and light reflected from the subject is focused as image information on the CCD by a focusing optical system. Then, the image information is photoelectrically converted into a desired image signal by the CCD.
The brightness of the edge of the image field represented by the light reflected from the subject or original is reduced by the cosine law and vignetting of the optical system. Since the image with such reduced brightness is focused on the CCD, the image signal is subjected to shading unless the reflected light is corrected.
Many proposals have heretofore been made for correcting the shading of images caused by a focusing optical system. According to one proposal, a light-shielding plate of a partly circular shape is disposed in the light path of illuminating light for linearly illuminating a subject or original along a main scanning line or the light path of light reflected from the subject, so as to reduce the amount of light reflected from the center of the main scanning line to a level lower than the amount of light reflected from the opposite ends of the main scanning line (see Japanese Laid-Open Patent Publications Nos. 56-62473 and 58-96453, for example). In another proposed arrangement, a slit having a width which is progressively narrower from the ends to the center thereof is disposed in front of an illuminating light source that is elongate along a main scanning line on a subject, for reducing the amount of illuminating light applied to the subject in the vicinity of the center of the main scanning line (see Japanese Laid-Open Patent Publications Nos. 56-107671, 58-146174, and 56-58364, for example).
With all of these prior art attempts, however, since the illuminating light is partly blocked or eliminated for shading correction, the efficiency of illumination of the subject or original is lowered, the image resolution by the CCD is reduced, and the device is costly to manufacture.
To solve the aforesaid problems of the conventional schemes, it has been attempted to construct an illuminating light source into a shape according to a pattern of shading of the image of a subject or original. That is, the opposite ends of the illuminating light source which is elongate along a main scanning line on a subject (original) are bent toward the center of the illuminating light source to increase the amount of light applied from the bent ends to the subject (see Japanese Laid-Open Utility Model Publication No. 60-94765). Another similar illuminating light source which is elongate along a main scanning line on a subject or original has opposite ends of double structure (see Japanese Laid-Open Utility Model Publication No. 60-109260).
These illuminating light sources are however very special in configuration, and hence cannot be mass-produced inexpensively.
Japanese Laid-Open Patent Publication No. 56-161773 discloses an illuminating light source capable of illuminating a subject or original efficiently with high illuminance. The illuminating light source comprises an array of LEDs disposed along a main scanning line on a subject and spaced at intervals which are progressively smaller from the center toward the opposite ends of the main scanning line. Inasmuch as the opposite ends of the main scanning line are illuminated with higher illuminance, any shading on the reproduced image of the subject is effectively corrected.
However, the disclosed illuminating light source has proven unsatisfactory in that the reproduced image suffers from density irregularities or variations inasmuch as the LEDs are positioned near the subject for higher illuminance on the subject and those LEDs which illuminate the central area of the main scanning line are relatively coarsely spaced.